1. Field of the Invention
The present invention relates to a liquid crystal display apparatus which achieves comparatively bright display, and more particularly, to a super twisted nematic (STN) liquid crystal display apparatus used as both reflection and transmission types. The invention also relates to a terminal apparatus using the liquid crystal display apparatus.
2. Description of the Related Art
In transmission-type, semi-transmission-type and reflection-type liquid crystal display apparatuses, the incident light passes through the polarizer at least twice before exiting from the liquid crystal display apparatus. The transmission-type liquid crystal display apparatus typically includes a pair of polarizers sandwiching at least a liquid crystal display device therebetween, and the light incident on the side of one polarizer exits from the side of the other polarizer. The reflection-type liquid crystal display apparatus typically includes a polarizer, a liquid crystal display device, a polarizer and a reflector disposed In this order, and the light incident on the side of one polarizer is reflected by the reflector to exit from the side of the other polarizer. For this reason, the transmissivity remarkably decreases, so that bright display is not obtained. Particularly, in the reflection-type liquid crystal display apparatus, there are shaded portions in the display because of a parallax due to the distance from the liquid crystal display device to the reflector. This markedly degrades the visibility.
Japanese Unexamined Patent Publication JP-A 6-230362 (1994), for example, discloses an art to solve the degradation of the visibility due to the parallax and an art to increase the brightness with respect to a reflection-type twisted nematic (TN) liquid crystal display apparatus. Specifically, on one side of the liquid crystal display device, a polarizer is disposed, and on the other side of the device, a 1/4 wave plate, a cholesteric liquid crystal polymer film and a light absorber are disposed in this order from the side of the liquid crystal display device to be in close contact with each other. Unnecessary light incident on the side of the polarizer is absorbed by the light absorber so that only light of one given wavelength again passes through the polarizer to exit. By using the 1/4 wave plate and the cholesteric liquid crystal polymer film as the polarizer on the side of the reflector and using the light absorber instead of the reflector to absorb the unnecessary light, the distance from the liquid crystal display device to the reflector is decreased to solve the degradation of the visibility due to the parallax, and by using only one polarizer, the brightness is increased.
"Asia Display '95 S47-3" (held on Oct. 7, 1995) discloses an art of applying a cholesteric reflective polarizer (CRP) in which a cholesteric liquid crystal film having a continuous pitch length and a 1/4 wave plate is combined, to a backlighting system for a transmission-type liquid crystal display apparatus comprising two polarizers sandwiching a TN liquid crystal display device therebetween. In this art, the CRP converts circularly polarized light into linearly polarized light which is supplied to the liquid crystal display apparatus.
In JP-A 6-230362 (1994), since the light incident on the side of the polarizer is reflected by the light absorber to again pass through the polarizer, the light incident on the liquid crystal display device has already passed through one polarizer, so that only 50% of the incident light is incident on the liquid crystal display device. The light from the liquid crystal display device is reflected and again passes through the polarizer via the liquid crystal display device, so that the amount of exiting light is further reduced to approximately 50% of the light incident on the liquid crystal display device. Thus, the use efficiency of the light is comparatively inferior. Additionally, in this prior art, since only polarized light of a specific wavelength is converted into circularly polarized light by the cholesteric liquid crystal polymer film, the coloration of the display occurs. In the arts disclosed in "Asia Display '95 S47-3", since a CRP is applied to a liquid crystal display apparatus comprising two polarizers sandwiching a liquid crystal display device therebetween, the use efficiency of the light is inferior.